There has existed for some time a need for thermally stable, elastomeric polymers for various aerospace and sealant applications. Also, for a polymer to satisfy the requirements, it must be hydrolytically stable and must retain its elastomeric properties at sub-zero temperatures. While silicone polymers have been suggested for such uses, they are not entirely satisfactory because of their hydrolytic instability. In U.S. Pat. No. 4,005,142, R. C. Evers recently disclosed perfluoroalkylene ether bibenzoxazole polymers possessing thermooxidative stability and having a low glass transition temperature (Tg). These properties render the bibenzoxazole polymers suitable for seal and sealant applications. Since the Tg of a polymer is an indication of the temperature at which it retains its elastomeric properties, it would be desirable to have polymers with even lower glass transition temperatures.
For a number of years it has been recognized that fluorocarbon elastomers, particularly copolymers of vinylidene fluoride and hexafluoropropylene, possess good mechanical properties, such as tensile strength and tear resistance, and high temperature stability. These properties make them especially attractive for use as O-ring seals in hydraulic systems. However, the poor low temperature flexibility of the elastomers limits their use in this application. Attempts to improve the low temperature flexibility of the elastomers to below -40.degree. F. have proven to be unsuccessful. For example, blending of the elastomers with commercially available low temperature flexible polymers have generally given blends possessing the worst properties of both components. To meet the advanced aerospace requirements of the future, there is a need for hydraulic O-ring seals that can meet the low temperature sealing requirement of -65.degree. F. while maintaining a satisfactory performance throughout the entire application profile.
It is an object of this invention to provide a fluoroalkyleneether silicate copolymer which possesses a high degree of thermal and hydrolytic stability and has a very low glass transition temperature.
Another object of the invention is to provide a blend of the copolymer and a fluorocarbon elastomer that has an increased strength and low temperature flexibility as compared to the fluorocarbon elastomer per se.
A further object of the invention is to provide a process for preparing the copolymer.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.